Cold Spray Tensile Strength Literature Review

Goals

To identify scientific literature that notes the tensile strength of cold spray combinations in order to bolster acceptance by potential customers. The pounds per square inch in the studies found must be 125,000 or higher and focused on the cold spray process.

Early Findings

  • While a 2007 article by the Air Force Research Laboratory titled “Mechanical and Microstructural Effects of Cold Spray Aluminum on Al 7075 Using Kinetic Metallization and Cold Spray Processes” did not specify tensile strength, it did note the following benefits of cold spray on performance: "Some limitations of conventional thermal spray processes are addressed by the cold spray process. Due to the high deposition temperature of conventional thermal spray processes, limitations exist with the substrate materials that can be coated. Coating materials that undergo phase transformations, recrystallization, excessive oxidation, and evaporation may be difficult or impossible to apply using conventional thermal spray methods. This is especially true for reactive materials such as titanium. Deformation or increased residual stresses induced by the thermal coefficient of expansion mismatch that develop as the coating and substrate cool down after deposition (or after each spray pass) are common in thermal spray processes. Even if the coating remains attached to the substrate, high residual tensile stresses may cause unacceptable distortions that significantly weaken the bond strength, accelerate fatigue failures, and introduce microcracking reducing the coating’s performance. Cold spray addresses some of these issues associated with conventional thermal spray techniques. The lower deposition temperatures reduce the effects associated with recrystallization in both the substrate and coating. Oxidation of metallic species is greatly reduced, which generally increases coating performance in corrosion environments. CS technology can be applied to a wider variety of substrates and residual stresses are generally compressive in nature, due to the physics of the impinging particles. Thick coatings can readily be built-up making cold spray technology a viable candidate for rapid prototyping. Noise levels are significantly lower and there are no dangerous metal vapor fumes (however, depending on the size of the powders, necessary precautions should always be taken to prevent inhalation).
  • While there was no specific reference to a PSI above 125,000 in terms of cold spray tensile strength, this 2017 study (“Characterization of Cold-Sprayed Copper Coatings and comparison with Wrought Copper using Miniaturized Shear Punch Tests”) noted some comparisons between shear strength and tensile strength of cold-sprayed copper (with 3 different orientations of coatings) and compared them to heat-treated coatings.
  • This 2017 book, titled “Cold-Spray Coatings: Recent Trends and Future perspectives,” may shed light on recent cold spray innovations.
  • While the current research has yet to identify a tensile strength of 125,000 or higher for a cold-spray material and substrate, Science Direct does provide a substantial literature review on the cold spray process that may be of interest. Another list is available here.

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